(1) Field of the Invention
The present invention pertains to motor shells or motor housings having separate enclosures attached thereto. In particular, this invention relates to motor shells having mounting tabs for use in mounting a separate enclosure to the motor shell and to a method of mounting an enclosure to a motor shell using mounting tabs integrally formed from the same piece of material which forms the motor shell.
(2) Description of the Related Art
Electric motors are used in a vast number of applications for converting electrical energy into mechanical motion. It is well known in the art to encase an electric motor in a shell or housing to protect the internal components of the motor from physical damage or interference. In many instances, a capacitor or other element must be electrically connected to the electric motor to ensure optimum performance. In those instances, the electrical element is external to the motor shell and is encased in its own enclosure. However, because the motor and the external element are sold as a single unit, the enclosure which encases the external element is typically secured to the outer surface of the motor shell. For example, it is common for an electric motor to have a capacitor cover attached to the outer surface of the motor shell to protect and support a capacitor which is electrically connected to the electric motor.
A motor shell is usually formed from a rectangular piece of material known in the art as a frame band. The frame band is usually made of a metallic material and is rigid to provide protection to the internal motor and insulate the moving components of the motor from external interference. Frame bands can be manufactured in large quantities through well known manufacturing processes. After they are manufactured, frame bands are usually stored in large quantities until they are needed to form motor shells. Because the frame bands are flat, relatively thin pieces of material they can be stored by stacking one on top of another thereby allowing storage of numerous frame bands in less space than that needed for preformed motor shells.
When needed to manufacture motor shells, the frame bands are formed into a cylindrical shape by well known manufacturing processes and the ends of the rectangular bands are welded together. The interior of the motor shell is hollow to allow the placement of a motor, such as a stator and rotor assembly, therein. After the motor is inserted into the motor shell, end caps are usually placed on the ends of the motor shell to complete the assembly.
After completion of the motor shell assembly, it is usually necessary to electrically couple a capacitor or other external element to the electric motor to enhance the motor's operating characteristics. This is usually accomplished by attaching the element to electric leads from the motor which protrude through holes in one of the end caps or through openings in the motor shell. Because the external element is exterior to the motor shell, a separate enclosure is usually required to protect and support the external element. In addition, electrical motors are packaged and sold with the external element as one unit, therefore, it is common to secure the enclosure to the motor shell.
Unfortunately, prior art devices and methods used in attaching an enclosure to a motor shell are inefficient, costly, and require additional manufacturing process steps to prepare the motor shell for attachment of the enclosure. In addition, the additional manufacturing steps occasionally damage the internal workings of the electric motor. When such damage occurs, additional costs are incurred due to the time and manpower required to restore the motors to their original condition.
One prior art method which is used to prepare a motor shell for attachment to an enclosure is to weld threaded studs to the external surface of the motor shell. The threaded studs are usually welded onto the outer surface of the motor shell after the formation of the motor shell into its cylindrical shape from the frame band. This requires an additional manufacturing step which cannot be incorporated into the manufacturing process of the frame bands. If bolts or studs were attached to the frame bands during the manufacturing process, the ease with which the frame bands are stored is diminished. Furthermore, the location and size of the studs or holes are determined by the type and size of the enclosure. The studs provide a projection from the outer surface of the motor shell onto which the enclosure, such as a capacitor cover, can be secured. The enclosures have flanges with apertures therein for receiving the studs. Nuts are usually threaded onto the studs after the enclosure is installed on the studs to hold the enclosure firmly in place.
Another prior art method for attaching an enclosure to a motor shell is to drill holes into the motor shell which correspond to the apertures in the enclosure flanges. Self-tapping screws or bolts can then be used to secure the enclosure in place on the motor shell. The screws are inserted through the apertures in the enclosure flanges and into the drilled holes in the motor shell. Although drilling holes in the motor shell could be performed when manufacturing the frame band, it is common to delay the drilling until the motor shell is formed into the cylindrical shape and even after the stator assembly is inserted into the motor shell. This process accommodates the use of many different types and sizes of enclosures which may not be determined until after the type of motor is determined. For example, the same size frame band can be used for a variety of different types of motors. Although the motors may be of the same size and therefore fit into the same size motor shell, different characteristics of the motor may call for different external elements for the particular motor. Due to the different characteristics of the external elements, such as size and placement, different types and sizes of enclosures must be used. Therefore, by waiting until the motor is placed into the motor shell, one can then determine the type and size of the external enclosure which is required and thereby determine the location of the holes to be drilled. Because different sizes and types of external elements can be used with a particular motor shell, it is impractical to always manufacture the frame bands with predrilled holes for threaded fasteners therein because too many holes would have to be drilled to accommodate all of the different types and sizes of enclosures.
Unfortunately, drilling holes into the motor shell after the motor is placed therein may cause damage to the motor. For example, it is not uncommon for the drill to displace or damage the stator teeth. The displacement of the stator teeth forces the teeth into the central bore of the stator assembly where the teeth may strike the rotor. Because the space between the stator teeth and the external surface of the rotor is extremely small, any extension of the stator teeth into the central bore of the stator assembly could cause the motor to fail. When this occurs, alternative procedures are required to repair the damaged motor. One such process, known as rollerizing, adds additional steps in the manufacturing process thereby adding to the cost. In addition, the damage is sometime so extensive that even the additional procedures are incapable of adequately repairing the motor.
As discussed above, the prior art devices and methods are inefficient, costly and tend to damage the motors thereby requiring additional work and expense. What is needed is a device and method that allow quick, reliable attachment of an enclosure, such as a capacitor cover to a motor shell without the problems of the prior art. Such a device and method would preferably require little change to the existing manufacturing processes and procedures and accommodate various different types and sizes of enclosures. In addition, the method should facilitate the attachment of an enclosure to a motor shell without requiring drilling or welding and without damaging the internal workings of a motor.